What is pH?
INTRODUCTION pH is defined as the concentration of hydrogen (H+) ions in solution. It is calculated mathematically by the formula: pH = -log10[H+], with the bracketed factor, [H+] being the concentration of hydrogen ions. So if there was a concentration of hydrochloric acid (HCl) of 0.01M (M = Molarity, a method for presenting concentration, defined as moles of a substance/liters), then pH of that HCl is: -log10(0.01) = 2.
The scale of pH is defined from 0 to 14. Pure water has a pH of 7, which is considered a neutral pH. Any pH below 7 is considered ‘acidic’, while any pH above 7 is considered ‘alkaline’, or ‘basic’.
As you get more acidic (closer to 0 on the scale), the number of H+ ions increases. As you get more basic, the number of H+ ions decreases. Step-wise changes of pH (from 5 to 4, or 8 to 9) involve an increase or decrease in the concentration of H+ ions by a factor of 10. So decreasing pH from 5 to 4 multiplies the number of H+ ions by 10-fold, and increasing pH from 8 to 9 decreases the number of H+ ions 10-fold.
Another important aspect of pH is that the H+ ion is not the only chemical entity worth considering. As pH becomes more basic/alkaline, H+ ions are decreasing in favor of hydroxide ions. Hydroxide ions (OH-) and hydrogen ions (H+) are the two ions that result from the self-ionization of water: H2O H+ + OH-. Simply, the more H+ ions there are, the more acidic a solution is, and the more OH- ions there are, the more basic a solution is. The chemistry behind why certain compounds elicit acidic solutions while others result in basic solutions is worth another paper entirely.
WHY DOES PH MATTER?
The range of pH levels in the human body is quite wide; our stomach acid has a pH of ~1, while some of the digestive enzymes secreted by our pancreas are over a pH of 8. Our blood is tightly regulated to a pH range of 7.35-7.45; it can go no higher or lower or medical maladies will result. Why does this matter? It is because extremes of pH (or even pH levels outside of physiological ranges) can wreck havoc on living cells and microbes. The reason our stomach acid has a pH of 1 is due to the fact that we ingest a number of bacteria with our food every day. This low pH serves as a very effective front line of defense against infection, disrupting the cell walls of these bacteria and destroying them. Why is bleach used as a disinfectant? Because it has a pH of ~13; this is deadly to living cells and microbes.
The method by which extremes of pH kill microbes and living cells can be simply presented, although there is significant chemistry behind it. The pH of stomach acid, at 1, has a very high concentration of H+ ions. These H+ ions do not want to be ions. Without going too far into the chemistry, it is very energetically favorable for these H+ ions to bond with another atom or molecule. As the number of H+ ions increases, it becomes more and more energetically favorable, to the point where these H+ ions will attack certain molecules and structures on microbes, disrupting the normal functioning of these microbes.
The same basic idea holds for the other end of the pH scale. OH- molecules will also attack molecules and structures on microbes, although in a different mechanism than H+ ions, rendering these microbes unable to function properly and effectively killing them. This is accomplished by disrupting the ability of these microbes to produce ATP. ATP is an energy-rich molecule that serves as an efficient way to store and use energy in all living cells. The disruption of important proteins needed to produce ATP is what kills these microbes. It is important to note that extremes of pH are also disruptive to most human cells; skin contact with a concentrated solution of hydrochloric acid or bleach will result in the painful destruction of your skin cells by the same methods presented above.
pH AND MICROBES
Bacteria and other microbes exhibit various tolerances to pH level. The effects of pH are based largely on how the structure of proteins are changed due to the large concentration of either H+ ions or OH- ions. Most microbes grow in a pH range between 6.0-9.0, although some microbes can exist outside this range. Some of these bacteria exist at a pH of up to 11, and as low as 1 (can survive stomach acid!). Creating an environment in which the pH is greater than 11 is certain to kill microbes that come into contact with it. This is important in sterilization uses, e.g. hospitals, lab equipment.
Solutions that exhibit extremes of pH in either direction can be very useful in killing microbes, especially those solutions that exhibit a very alkaline pH. A cleaning solution with a pH of 12 would be very effective at killing microbes.
SIMIX Multi-Surface Coating (pH above 11) and SIMIX All Purpose Cleaner (pH above 12) are your complete surface solutions.